A minimum energy optical network is considered to be one that provides point-to-point connection for every pair of end-users. In such a network, each user can transmit to only one other receiver at a time and only the optical transmitter (laser) that is currently transmitting is turned on at any given time. However, given the large number of separate optical channels to choose from, the user node must include a device capable of selecting the proper optical channel and routing the communication payload originating from the user premises equipment (such as a personal computer), to the selected optical transmitter. Similarly, the user node must include a device capable of buffering and delivering to the user, the payload received through each one of its optical channels.
These functions are implemented by certain electronic circuitry. Given that complementary metal-oxide-semiconductor (CMOS) is, and is expected to remain the most energy-efficient electronic technology in the foreseeable future, the best implementation of the transmitting router for the minimum energy optical network should be based on digital CMOS circuits. For the same reason, a receiver at every user node of the minimum energy optical network should also be a digital CMOS circuit.
However, the choice of the implementation technology is not a sufficient guarantee for high energy efficiency of a circuit. In fact, the design of the two devices described above is rather challenging assuming that a large number of optical fibers is originating from one user node. In a conventional implementation, the device on the transmit side would appear as a large 1-to-N digital demultiplexer, where N is the number of optical fibers. As shown in FIG. 2, a 1-to-N demultiplexer 20 would consist of approximately 2N digital 1-to-2 demultiplexers 10, whose logic function is illustrated in FIG. 1 using two two-input NAND gates 12, 14 and one inverter 16. It can be seen from FIG. 2 that each demultiplexer is controlled by one from the set of ‘select’ signals tsel_1 22, tsel_2, tsel . . . k, where k=log 2(N). As a result of this control scheme, each time a new route is selected between the user interface and one of the optical fibers, the ‘select’ signals will change, causing energy dissipation in the 1-to-2 demultiplexers. Assuming that, on the average, one half of the ‘select’ signals change its state and that there are ˜2N demultiplexers, the total dissipation will be proportional to N.
The conventional implementation of the receive routing device is an N-to-1 multiplexer 40 shown in FIG. 4, which consists of about 2N 2-to-1 multiplexers 30, whose logic function is shown in FIG. 3. The logic function is depicted as consisting of 3 NAND gates 32, 34 36 and one inverter 38. Similar to the control in the conventional implementation of the transmit device, the multiplexers in FIG. 4 are controlled by a set of ‘select’ signals rsel_1 42, rsel_2, . . . rsel_k, where k=log2(N) and the resulting dissipation is proportional to N.
The prior art circuits of FIGS. 1 to 4 represent the logic functions for known demultiplexer and multiplexer systems. It will be apparent to a person skilled in the art, that these logic functions can be implemented by many alternative circuits to the ones depicted in these figures.
What is required is a routing device with lower energy dissipation than the conventional routing devices discussed above.